DC power is the most frequently used voltage source for electronic equipments. For the use of electronic equipments with different driving voltages, a DC-DC converter usually will be used to change the magnitude of a voltage. Please refer to FIG. 1, which is a well-known DC-DC voltage converter. It is composed of a bandgap 1, a pumping CKT 2, and a regulator 3. A user can choose the properties of the components according to the required supply voltage. Assume that the user needs a 7.2v output voltage Vout and a 2.4˜3.6 system voltage Vcc, who may choose a 1.2v bandgap 1 and a six-times pumping CKT 2. The system voltage Vcc is first dropped to 1.2v by the bandgap 1, then is pumped to the 7.2v output voltage by the six-times pumping CKT 2, finally is regulated by the regulator 3 to supply the regulated 7.2v output voltage Vout. If customers do not mind the slight variation of the voltage, the regulator 3 can be not used.
The aforementioned voltage converter, which is dropped by the bandgap 1 and then pumped by the multiple pumping CKT 2 such that the power consumption is quite serious. Therefore, please refer to FIG. 2, an operation method that directly uses the system voltage Vcc to be the source voltage of the pumping CKT 2 has been developed recently. Similarly assume that the user needs a 7.2v output voltage Vout and a 2.4˜3.6 system voltage Vcc, who only needs a triple pumping CKT 2, then regulated by the regulator 3 to supply a regulated 7.2v output voltage Vout. As a result, the operation efficiency for the pumping CKT 2 can be improved and the total power consumption is reduced.
In case the working voltage for the system voltage Vcc has a wider range whereas the operation method that directly uses the system voltage Vcc to be the source voltage of the pumping CKT 2 has to be adopted. For example, assume that a 5.0v output voltage Vout is needed whereas the system voltage Vcc is 2.0v˜3.6v, uses double pumping CKT 2 when the system voltage Vcc=3.0˜3.6v; uses triple pumping CKT 2 when the system voltage Vcc=2.0˜2.5v; when the system voltage Vcc=2.5˜3.0v then the multiple for the pumping CKT 2 should be switched between double and triple. Moreover, by way of the regulator 3 to drop and regulate the output voltage Vout can be regulated at 5.0v. Although this operation method can be applied on the case of wider system voltage Vcc, but when the system voltage Vcc=2.5˜3.0v then the multiple for the pumping CKT 2 will switch between double and triple, which substantially affects the voltage-converting efficiency.
Obviously, the aforementioned DC-DC voltage converter can supply voltage in accordance with the user's requirements. However, voltage-drop is unavoidable during the process of the voltage converting so as to supply the required voltage to the load, which leads to the unnecessary power consumption.